The present invention relates to a method for the deflection or bending of a beam of monopolar charged particles, in particular of electrons in which in a first direction perpendicularly to the direction of propagation of the beam flux density field is applied in order to deflect beam into a second direction perpendicular to the first and to the direction of beam propagation.
Such a method is known from U.S. Pat. No. 4,064,352. In that patent an electron beam from an electron beam gun used for the vaporization of a target material, is deflected by more than 180.degree. by disposing on both sides of the beam path, pole shoes of a magnetic pole arrangement between which a deflection field is generated. The electron beam therein extends by sections above the front faces of the pole shoes and consequently is located within a with curved lines of force of said field.
Such a deflection method is disadvantageous as will be explained in conjunction with FIG. 1. In FIG. 1 two magnetic poles 1 forming a magnetic dipole are represented schematically. The result is the flux density field B represented qualitatively which extends in the region of the dipole axis A as a straight line between the magnetic poles 1. If according to the cited U.S. Pat. No. 4,064,352 a beam of charged particles such as electron beam 3 is guided essentially in the plane of symmetry E perpendicularly to the dipole axis A between the magnetic poles 1, the charged particles experience a deflection force F as drawn in FIG. 1. This deflection force is employed to deflect the electron beam according to the cited U.S. Patent. If the position of the beam of charged particles is offset with respect to the plane of symmetry E as shown at 3b, deflection forces F.sub.b result which, in contrast to the force F.sub.a relative to the dipole axis A, have a transverse and a longitudinal component whereas in the case of the beam 3a located in the plane of symmetry E only a transverse component to axis A is generated.
It is evident that a coupling exists between the position of the beam in the direction of the dipole axis A and the deflection transversely to this axis A. Furthermore at a given flux density field and on shifting of the position of the beam in the direction of the dipole axis A, as shown in dot-dash lines, the beam cross sections are also influenced; different forces act at different regions of the cross-sectional area of the beam.
A further disadvantage can be seen in that on position change of the beam parallel to the axis A the absolute magnitudes of the resulting forces F change because the beam is not shifted along the lines of force of the field where the magnitude of the field vectors would be constant.
U.S. Pat. No. 3,420,977 discloses a method which either does not have the stated disadvantages or has them to a lesser extent. Here, a deflection flux density field is generated by magnetic pole shoes and the beam of charged particles, again electrons, is guided between the pole shoes. The extended pole shoes generate a field with only slightly curved lines of force. Consequently the electron beam 3 as shown in FIG. 2, is rather shifted along the dipole axis A. In the ideal case, always constant transverse forces relative to axis A, result.
This arrangement, in turn, has however the disadvantage that precisely when deflecting a beam by a large angle such as by 180.degree. and /more, for example by 270.degree., the magnetic arrangement becomes voluminous because the pole shoes must accept the beam between them along long regions. The pole shoes are also subjected to the effect of the beam on a target object, in particular the vaporization of materials to an increased degree. Moreover, the extent to which the beam can be shifted transversely to the shoes on the target object such as the crucible to be vaporized, is a function of the distance and the length of the shoes.
The disadvantages of the known approaches thus fundamentally rest with the fact therein that the regions of the deflection flux density field having curved lines of force and being thus inhomogeneous field regions, are not suitable for beam guidance as explained in conjunction with FIG. 1.